The present invention relates generally to systems for testing motor vehicle braking systems and more specifically to such systems which are specifically designed to test in a production line environment anti-skid braking systems presently being employed on some motor vehicles.
Production line testing of conventional vehicle braking systems has long been accomplished by means of power actuated devices which act against the vehicle brake pedal and operate to depress the brake pedal by means of applying a constant predetermined force thereto. Any leakage within the conventional hydraulic braking system is detected by measuring additional movement of the pedal during the test duration. Because the brake system is operated by means of fluid pressure generated directly by force applied to the brake pedal, any leakage from the brake system will result in increased pedal travel during the time period in which the force is maintained on the brake pedal. Accordingly, this approach has provided a simple and reliable method for testing the integrity of such conventional hydraulic brake systems.
In order to improve a motor vehicle operator's ability to bring a motor vehicle to a stop within a minimum distance and without loss of control, improved braking systems have been developed which include means to sense the rate of deceleration of the vehicle wheels and to alternately and cyclically release and reapply the braking action to any wheel experiencing an excessively high rate of deceleration. Such improved braking systems are commonly referred to as anti-skid braking systems and are presently being employed on certain models of motor vehicles presently offered for sale.
One form of such anti-skid braking system presently being offered on motor vehicles employs an electrically driven hydraulic pump which cyclically operates to generate a pressure in an accumulator associated therewith. Pressure from this accumulator is then selectively fed to the rear brakes of the motor vehicle and operates to actuate these rear brakes as well as to provide a power assist to operation to the front brakes of the vehicle. The primary operating force for application of the front brakes in this system relies upon the direct linkage between the vehicle brake pedal and the respective wheel cylinders/calipers via the master cylinder all in accordance with conventional braking systems. However with respect to the rear braking system, this is operated entirely by the pressure generated by the hydraulic pump and stored in the associated accumulator, there being no direct fluid nor mechanical linkage between the brake pedal and associated braking system.
Thus, because the anti-skid braking systems do not employ any direct mechanical or fluid interconnection between the brake pedal and the fluid system actuating the rear brakes, it is not possible to test the integrity of such systems in the manner previously employed as noted above. It should also be noted that in order to test such systems, it is desirable not to disconnect or otherwise break into the closed fluid system employed for actuation of the rear brakes due to both the time required to disconnect and reconnect the system as well as the potential that a leak may result should the reconnection not be made in a secure manner. It is also desirable to avoid the necessity to permanently include any additional sensing means as an integral part of the motor vehicle as the inclusion of such sensing means not only would require additional connections which may give rise to points of leakage from the system, but also would result in increased overall cost to manufacture the motor vehicle.
Accordingly, the present invention provides a method and apparatus for carrying out this method whereby such anti-skid braking systems may be easily and efficiently tested to assure that all connections associated therewith are fluid tight as well as to insure that various portions thereof are operating in accordance with the design specifications intended for such systems. The present invention incorporates sensor means to sense the duration and frequency of operation of the electrically driven hydraulic pump which sensor means operate in conjunction with means operative to sequentially and cyclically depress the motor vehicle brake pedal. In addition, the motor vehicle brake pedal operating means includes sensor means to sense the distance travelled by the brake pedal during each successive operation and to provide a signal indicative of this distance which is then compared with a prior signal to determine if the distance of travel falls within a predetermined range. Thus, by sensing the duration of operation of the hydraulic pump, it is possible to determine if the hydraulic pump is properly genreating the required pressure as well as determination of a possible defective pressure sensor within this portion of the system. The sensing of the distance of travel of the brake during successive operations provides an indication of any potential leaks within the brake actuating lines which would result in premature decrease in the pressure within the system. Further, continuous monitoring of the operational condition of the hydraulic pump will provide a further indication of leakage within the system resulting in premature pressure loss.
Thus, the present invention provides both a method and apparatus for carrying out this method which is particularly well suited for use in a production line environment in that it entails a relatively minimal amount of interconnection with the motor vehicle as it is moving down the production line and also incorporates a method which may be carried out in a relatively brief time period thus avoiding any excessive delays in movement of vehicles along the production line.